Weed Scientist: Poison Hemlock is a Manageable Menace

Poison hemlock is a problem for both livestock and row-crop producers, but can be eliminated without causing damage if identified in its first year of growth, a Purdue Extension weed scientist says.

Poison hemlock, aptly named for its toxicity to livestock, can also wind up in corn and soybean fields where it competes with the cash crop for resources, such as soil nutrients and water.

"It poses the risk of livestock poisoning or death if it is ingested by animals," Travis Legleiter said. "When present in high amounts along fence rows, it has also been known to creep into corn and soybean fields in the state."

Legleiter said there are a few ways to identify poison hemlock and distinguish it from two other plants it closely resembles: Queen Anne's lace and wild carrot. Poison hemlock can be spotted by its finely divided, triangle-shaped leaves and small, white flowers that grow in an umbrella shape and don't bloom until the weed's second year of growth. It differs from the other two weeds in that it displays purple splotches on its stem and lacks dense hairs.

Poison hemlock is usually found in areas of perennial crops such as pasture, fencerows and roadsides. Though it has been around for a while, the weed's prevalence on roadsides has recently been increasing.

In order to effectively manage poison hemlock, Legleiter said farmers need to identify it in its first year of growth when it is a low-growing rosette with green leaves and no flowers. While the weed is often not noticed in its first year, that's the time when the plant is most susceptible to herbicides.

Legleiter said herbicides most effective in managing poison hemlock are those containing triclopyr or 2,4-D as active ingredients.